Indices API: fixes GET Alias API backwards compatibility

For just the case when only the aliases are requested, the default indices options are to ignore missing indexes. When requesting any other feature or any combination of features, the default will be to error on missing indices.

Closes #7793
I don't think we should move it to the `GetIndexRequest#indicesOptions` getter as these are only the defaults and need to be overridden by the users request. I agree that we should have the same behaviour on both the REST and the transport layer so I'll move this logic to `TransportGetIndexAction`